Prestressed concrete structures



March 22, 1966 1 MAGERs, .1R 3,241,278

PRESTRESSED CONCRETE STRUCTURES Filed March 28, 1961 ATTORNEYS UnitedStates Patent O 3,241,278 PRESTRESSED CONCRETE STRUCTURES Leroy Magers,Jr., West Caldwell, NJ., assigner to The Preload Company, New York, N.Y.Filed Mar. 28, 1961, Ser. No. 98,954 4 Claims. (Cl. 52-224) Thisinvention relates to improved prestressed concrete structures and, inparticular, to the protection of the tendons used to prestress thestructures.

Prestressed concrete structures are widely used for many purposesincluding storage tanks, silos, reinforcing rings for dome top roofs,and other substantially cylindrical structures. Cylindrical prestressedconcrete structures are generally constructed by first erecting anannular concrete core wall or ring which may or may not be reinforced.In the case of a wall, a suitable foundation is constructed before thewall is erected. When a dome ring is to be constructed the supportingwall for the ring must also be first erected.

About the core wall or ring a series of convolutions of prestressingtendons are positioned. These tendons are tensioned and elongated acontrolled amount so that the concrete wall or ring is'radiallycompressed and has a resultant post-tension stress developed therein.Since the wall is subjected to radial compressive forces, it isnecessary that the wall be of sufficient thickness to withstand thestress.

The tendons are generally formed from high tensile strength steel wires,rods, lcable, or strand.

Such steel tendons are easily subjected to corrosion unless adequatemeasures are taken to protect them. Heretofore, the standard method ofprotection has been to coat the tendons with a material of cementitiousnature, usually mortar. The mortar coating is applied over the tendonsby means of a mechanical spraying apparatus or by building a form aboutthe tendons and pouring mortar into the form.

One of the problems with mortar coatings has been the problem of c-racksand leaks developing in these coatings. When this occurs, moistureenters into the cracks and corrodes the steel tendons. Also, in the caseof tanks, cracks sometimes occur in the concrete core wall. Such crackspermit liquid such as water to leak out and seep between the wall andthe mortar coating causing corrosion of the tendons. This internalleaking creates a serious problem due to the fact that the leak mayoccur in one portion of the wall and travel a substantial distancearound the tank before seeping out through the coating.

Such leaks are not only difficult to locate but highly costly to repair.This creates a serious maintenance problem and heretofore it hasdeferred some potential users of prestressed concrete tanks from usingsuch constructions.

In the present invention it is contemplated that a cementitious coatingof the entire tank may be eliminated if desired. To accomplish this, thetendon is advantageously enveloped with a protective wrapping or sheathduring the prestressing operation when the tendon is applied to the tankor, if desired, before it is applied. By so protecting the tendons witha fatigue and abrasive resistant material, such as polyvinyl chloride,the tendons are protected from atmospheric attack or humidityconditions. Fu-rther, the tendons are easily inspected and if cuts ortears occur in the coating, repairs may be quickly and easilyaccomplis-hed. If desired, the coating material may be transparent or atleast translucent, so that any discoloration of the tendon by corrosionmay be easily noted and repairs made before the st-ructural strength ofthe tendon is impaired.

A prestressed tank with coated tendons has an advan- ICC tage of beingmore economical to construct than the prior art structures, as well asbeing easier and more economical to maintain. In addition, if a leakoccurs in the concrete core wall, it may be easily located., and quicklyrepaired without the necessity of removing large portions of a mortarcoating.

In the accompanying drawings and in the speciiication severalembodiments of the present invention are shown. It is to be understoodthat these embodiments are for the purpose of illustration and they arenot to be construed as limiting the present invention, but rather theyare for the purpose of disclosing the invention to those skilled in theart so that it may be practiced in various embodiments, each within thespirit and scope of the invention as claimed herein.

In the drawings:

FIGURE l is a perspective view of a prestressed concrete tankconstructed in accordance with the present invention;

FIGURE 2 is a fragmentary sectional view of a core wall of the tankshowing a coated prestressed strand element tensioned against the wall;

FIGURE 3 is a fragmentary sectionalview of the core wall of the tankshowing a coated prestressed solid tendon againstrthe core wall; r

FIGURE 4 is a fragmentary sectional view of the core wall showing atendon band of several wires encapsulated in a protective lm positionedagainst the clore wall; and

FIGURE 5 is a fragmentary view of the core wall and tendon band ofFIGURE 4 in the direction of lines 5-5 of FIGURE 4.

Referring to the drawings and to FIGURE l in particular, a tank 10 isshown which is comprised of a footing 12, a concrete annular core wall14, prestressing tendons 16 encircling the wall and a dome ring 18 whichsupports a dome shaped roof 20. The tank 10 is erected by firstconstructing the footing 12. The concrete core wall 14 is then placedand when it has set the wall is prestressed by wrapping it with a seriesof convolutions of high tensile strength tendons 16, such as steelwires, rods, -cable or strand. Means and methods for wrapping thetendons 16 about the tank wall in order to prestress them are well knownin the art. Such automatic prestressing apparatus and a method of usingit is shown in US. Patent No. 2,364,696. Another method of tensioning;the tendons about the tank wall is shown in the copending application,Serial No. 60,682, led October 5, 1960, now Patent No. 3,123,942, andassigned to the same assignee as the present application.

With the annular wall 14 in place the dome roof 20, may be erected andprestressed by means of the dome ring 18. The dome ring 18 is anextension of the wall 14 and is generally characterized by aconstruction which is comprised of a number of tendons wrapped about theupper portion of the wall 14 so that the roof 20 is prestressed andplaced under tension.

As shown in FIGURE l, no protective coating is required to be placedover the entire tank wall 14. The necessity for such a coating iseliminated by use of a protective sheathing of suitable plastic materialwhich is formed about the steel core of the tendon 16 and protects itfrom corrosion.

In FIGURES 2, 3, and 4, several embodiments of coated tendons are shown.

In FIGURE 2, a coated tendon 16a is shown which is comprised of a strandsteel core 22, about which is placed a suitable coating 24. The coating24 is advantageously made of a scuff and abrasive resistant flexibleplastic which is fatigue resistant and substantially unaffected byatmospheric attack or humidity conditions. A suitable plastic materialis plasticized polyvinyl chloride or copolymers thereof such aspolyvlnyl chloride-acetate copolymers.

In FIGURE 3 a solid rod or heavy Wire 26 serves as the core for thetendon 16h. A similar plastic coating 23 is placed about the core 26 andprotects it from corros1on.

In FIGURE 4 several fine wires 30 are encapsulated in la plastic sheet32 to form a band-like tendon 16C. In using tendon 16C, the wires 30 andcoating 32 are prefabricated and cut to a predetermined length beforebeing applied to the tank. To apply the tendon 16e` the plastic and wirebelt combination is wrapped around the tank and the ends drawn togetherby suitable means such as jacks, torque wrenches, etc.

In FIGURE 5 a joint formed in a belt combination tendon 16C is shown.Attached to each end of the tendon 16C is a flange 34 to which the wires30 are anchored. When the untensioned tendon 16e is first placed aboutthe tank the flanges 34 are spaced apart a substantial distance. Byjacking the anges together and welding them in place at 36, apredet-ermined elongation of the wires 30 is achieved, with thecorresponding tensile strength also being developed ltherein. If theplastic coating 32 is not suciently stretchable to be elongated to thesame extent as the steel wires 30 a filler patch of plastic material maybe applied between the flanges 34 and the end of the plastic material sothat the entire length of the wires 30 will be coated.

In prestressing the tendons 16 a permanent elongation ils obtained and atensile stress developed in the steel core in the order of about 120,000p.s.i. While the tensile stress developed in the steel core is quitehigh, the radial force developed by the tendon against the concrete wallis quite low. This radial force is not suflicient to extrude the plasticcoating of the tendon to a point where the core is uncoated.

The present invention provides a tank construction which is economicalto build and easy to maintain.

I claim:

1. A substantially corrosion resistant cylindrical concrete structurecomprising an annular wall of substantial thickness and sufficient towithstand forces applied thereto, a series of convolutions of hightensile strength tendons wrapped about the outer face of the wall undersubstantial tension, said tendons being elongated a desired amountwhereby the concrete wall is prestressed and circumferentiallycompressed by the radial pressure exerted by `the tensioned tendons, anda preformed, flexible and scuff and abrasive resistant plastic coatingcompletely enveloping each tendon and applied thereon before saidtendons are wrapped and tensioned about the wall, a portion of saidcoating being positioned between the outer face of the wall and thetendon, said plastic having Sullicient resistance to extrusion to resistthe radial force developed by the tendon whereby the tendon remainsenveloped in the plastic coating under said Aradial force.

2. A substantially cylindrical concrete .structure as defined in claim 1wherein said tendon has a solid core of high tensile strength steel.

3. A substantially cylindrical concrete structure as dened in claim 1wherein said tendon has a strand core of high tensile strength steel.

4. A substantial cylindrical corrosion resistant concrete structure asdened in claim 1 wherein each of said tendons has a core of high tensilestrength steel and said steel has a tensile stress developed therein inthe order of about at least 120,000 p.s.i.

References Cited by the Examiner UNITED STATES PATENTS 702,738 `6/1902Montgomery 285-236 1,189,694 7/1916 Janssen et al. 52-224 1,383,1666/1921 Steinkraus 52--224 2,185,749 1/1940 Kennedy 52--224 2,193,7143/1940 Covey 52-192 2,315,895 4/1143 Crom 52-224 2,411,651 11/1946 Darby52-82 2,579,183 12/1951 Freyssinet 52-224 2,597,084 5/1952 Huddleston52-224 2,722,237 11/1955 Rosel 138-174 2,803,868 8/1957 Dobell 52-224 X2,850,890 9/ 1958 Rubenstein 5 2 229 2,918,314 12/1959 Kernnitz 285-1492,932,964 4/1960 Dobell 52-224 2,992,131 7/1961 Bricknell et al. 52-7273,022,713 2/1962 Friberg 52-230 FOREIGN PATENTS 184 12/ 1906 GreatBritain.

r FRANK L. ABBOTT, Primary Examiner.

WILLIAM I. MUSHAKE, JACOB L. NACKENOFF, Examiners.

1. A SUBSTANTIALLY CORROSION RESISTANT CYLINDRICAL CONCRETE STRUCTURECOMPRISING AN ANNULAR WALL OF SUBSTANTIAL THICKNESS AND SUFFICIENT TOWITHSTAND FORCES APPLIED THERETO, A SERIES OF CONVOLUTIONS OF HIGHTENSILE STRENGTH TENDONS WRAPPED ABOUT THE OUTER FACE OF THE WALL UNDERSUB STANTIAL TENSION, SAID TENDONS BEING ELONGATED A DESIRED AMOUNTWHEREBY THE CONCRETE WALL IS PRESTRESSED AND CIRCUMFERENTIALLYCOMPRESSED BY THE RADIAL PRESSURE EXERTED BY THE TENSIONED TENDONS, ANDA PREFORMED, FLEXIBLE AND SCUFF AND ABRASIVE RESISTANT PLASTIC COATINGCOMPLETELY ENVELOPING EACH TENDON AND APPLIED THEREON BEFORE SAIDTENDONS ARE WRAPPED AND TENSIONED ABOUT THE WALL, A PORTION OF SAIDCOATING BEING POSITIONED BETWEEN THE OUTER FACE OF THE WALL AND THETENDON, SAID PLASTIC HAVING SUFFICIENT RESISTANCE TO EXTRUSION TO RESISTTHE RADIAL FORCE DEVELOPED BY THE TENDON WHEREBY THE TENDON REMAINSENVELOPED IN THE PLASTIC COATING UNDER SAID RADIAL FORCE.